1. Field of the Invention
The present invention relates to a photosensitive composition suitable as a resist material used in micropatterning in the fabrication of semiconductor devices.
2. Description of the Related Art
In the micropatterning of various electronic parts including semiconductor integrated circuits such as LSIs, micropatterns are formed by photolithography using resists. In especially recent years, as the numbers of types and functions and the density of electronic devices have increased, the formation of finer resist patterns is being required. One method of forming finer resist patterns is to shorten the wavelength of an exposure light source. In a recently developed resist pattern formation technology, short-wavelength light such as an ArF excimer laser (193 nm) or a quintuple harmonic (213 nm) of a YAG laser is used as an exposure light source.
Unfortunately, common resist materials transmit light in this wavelength region only about 1/30 .mu.m. Accordingly, exposure light cannot well reach a portion apart from the surface of a resist film during exposure. Consequently, it is difficult to form micropatterns by using resist materials of this sort even when short-wavelength exposure light is used.
To form a fine pattern by fully utilizing the effect of exposure light with a short wavelength, the use of a resist having high transparency to light of that wavelength is essential. Also, to more effectively perform micropatterning for a wiring pattern by using the obtained resist pattern as an etching mask, the resist must have high resistance to dry etching.
As a resist material having a high light transparency, Jpn. Pat. Appln. KOKAI Publication No. 4-39665 has disclosed a resist containing a copolymer of a polymerizable compound having the alicyclic hydrocarbon side-chain and a polymerizable compound with an alkali solubility. Although this resist has high light transparency and high dry-etching resistance, the solubility of the resist in a developer is not sufficiently high. That is, the resist contains a copolymer of an alicyclic compound with no alkali solubility and a carboxylic acid compound with a very high alkali solubility, i.e., two polymerizable compounds having the two extremes of physical properties. Therefore, during development only an alkali-soluble portion unavoidably dissolves to result in nonuniform dissolution. As a consequence, a high resolution is difficult to obtain, cracks or roughened surfaces readily form due to partial dissolution in unexposed portions, and the reproducibility of pattern formation is also low. Furthermore, a developer enters the interface between a resist film and a substrate and destroys the pattern in the worst case. Additionally, a copolymer of the above sort readily brings about phase separation and nonuniformly dissolves in a solvent. This makes the choice of a coating solvent very difficult and degrades the coating properties on a substrate.
As described above, a resist material is being desired which has high transparency to short-wavelength light such as an ArF excimer laser, high alkali solubility, high resolution, high reproducibility, and high dry-etching resistance necessary for micropatterning. However, no resist material meeting all these conditions has been developed yet.